This chapter introduces a new climatology index, the Caspian Sea—Hindu Kush Index (CasHKI), which consists of changes in the mean sea level pressure (MSLP) gradient between the Caspian Sea (CS, 40–50 °N, 50–55 °E) and Hindu Kush (HK, 35–40 °N, 70–75 °E) which modulate the atmospheric dynamics and dust activity over southwest (SW) Asia. The CasHKI is defined as the difference between MSLP anomalies over the CS and HK (MSLPanom.CS—MSLPanom.HK) and is initially examined during the summer months (June-September, JJAS) of 2000– 2014. The NCEP/NCAR data for MSLP and surface meridional wind, along with IDDI (Infrared Difference Dust Index) retrievals from Meteosat, OMI-AI and TRMM rainfall products and SPRINTARS model simulations of dust emissions are analyzed as a function of CasHKI. The CasHKI variations modulate the atmospheric dynamics over SW Asia. Increase in CasHKI intensity strengthens the northerly flow along the eastern Iranian borders (Levar wind), resulting in activation of the dust sources over the region and in significantly larger dust outflows over the northern Arabian Sea. Extending the research to the whole year, during the enlarged period 1963–2014, verifies the role of the CasHKI as a regulatory factor for dust activity over SW Asia, even during the winter period.